Interpretive Summary: A line of miniature Brahman cattle at the USDA, ARS, STARS in Brooksville, Florida have been characterized as having normal proportioned growth but are approximately two-thirds in frame size and body weight as that of normal Brahman at maturity. Furthermore, these miniature Brahman were reported to have abnormally high circulating concentrations of growth hormone (GH) and abnormally low circulating concentrations of insulin like growth factor-I (IGF-I) compared to normal Brahman contemporaries. These hormone differences are similar to a condition in humans termed Laron dwarfism. Subsequent studies in reproduction and growth aspects were conducted to more fully understand the mechanism associated with this anomaly. Results from earlier studies indicated that administration of GH or increased endogenous GH did not elicit an effect on IGF-I in growing miniature animals. Furthermore, miniature Brahman had lower circulating concentrations of insulin and a blunted or delayed rise in insulin after meal feeding as compared to normal Brahman contemporaries. Therefore in this study, we hypothesized that IGF-I secretion could be enhanced by concomitant administration of exogenous GH and insulin, and neither alone would be effective. However, results indicated that in the miniature Brahman model, both GH and GH + insulin treatments increased IGF-I in mature cattle, suggesting that this line of Brahman cattle is capable of responding to bioactive GH. In a parallel study, we previously reported that miniature Brahman cattle were homozygous for a single nucleotide polymorphism in GH that encodes a mutation in an amino acid involved in binding of GH to the GH receptor.